1. Field of the Invention
The present invention relates to a battery case of an electronic device in which different types of batteries having different shapes can be selectively used as a power source for the electronic device.
2. Description of the Related Art
Many electronic devices, especially cameras of recent years, have been designed to use a special battery exclusive thereto. For instance, lithium primary batteries are higher in weight energy density and volume energy density than lithium secondary batteries, and are accordingly, suitable as a power source especially for high-power consumption electronic devices such as digital cameras. However, since there are few manufacturers of lithium primary batteries developed specially for cameras, and since adequate sales outlets for such lithium primary batteries have not yet been established, it is hard to find the lithium primary batteries, especially in foreign countries, which causes inconvenience to the user when they use the camera. Consequently, various cameras have been made available to the market in recent years for which not only general-purpose primary lithium batteries and an exclusive secondary lithium battery but also general-purpose AA-sized cells that are easy to attain even in foreign countries, are available as a power source. For instance, in Japanese unexamined patent publication 2002-208387, a part of a camera body which surrounds a battery case (battery compartment) for accommodating an exclusive battery is constructed as a withdrawal battery-chamber forming member so that AA-sized cells can be accommodated in the battery case instead of the exclusive battery if the battery-chamber forming member is drawn out. This structure enables the camera to work on easy-to-get AA-sized cells.
A digital camera provided by the assignee of the present invention is also constructed to run on not only an exclusive battery (lithium primary battery) but also on AA-sized cells. FIG. 1 shows such a digital camera. As shown in FIG. 1, a camera body 1 is provided in a grip portion 3 thereof with a battery case 10 that forms a battery chamber. The battery case 10 includes a battery chamber lid 12 which is supported in hinged relationship to a bottom wall 1a of the camera body 1 so that the battery case 10 is closed and opened by closing and opening the battery chamber lid 12 when a battery is loaded and unloaded into and from the battery case 10. In a closed state of the battery chamber lid 12, sliding the battery chamber lid 12 slightly rearward in a direction shown by an arrow B1 in FIG. 1 relative to the camera body 1 causes the battery chamber lid 12 to be engaged with the bottom wall 1a to thereby be locked relative to the bottom wall 1a . In this digital camera, either four AA-sized cells or two CR-V3 batteries (lithium primary batteries) can be selectively accommodated in the battery case 10 since the digital camera is made to run by a six-volt power source. As shown in FIG. 15A, the AA-sized cell D1 is in the shape of a cylinder having a predetermined diameter d1 and a predetermined length L1 and is provided at upper and lower ends thereof with a positive electrode (+) and a negative electrode (−), respectively. On the other hand, the CR-V3 battery D2 has a shape corresponding to the shape of two AA-sized cells arranged side-by-side parallel to each other as shown in FIG. 15B, and accordingly, the thickness d2 of the CR-V3 battery D2 is substantially identical to the diameter d1 of the AA-sized cell D1. However, the length L2 of the CR-V3 battery D2 is greater than the length L1 of the AA-sized cell D1 (approximately 2.5 mm) and the CR-V3 battery D2 has a positive electrode (+) and a negative electrode (−) which are positioned side by side at an end surface of the CR-V3 battery D2.
To make the camera capable of selectively using four AA-sized cells or two CR-V3 batteries, the battery case 10 is shaped so that four AA-sized cells can be loaded into the battery case 10 in a two-by-two parallel arrangement and so that two CR-V3 batteries can be loaded into the battery case 10 with the two CR-V3 batteries arranged side-by-side in the direction of the thickness of the CR-V3 batteries. Additionally, although not shown in the drawings, springy metal contacts which are contactable with associated electrodes of the batteries accommodated in the battery case 10 are fixed to an inner surface of the battery chamber lid 12. The springy metal contacts are brought into contact with the associated electrodes of the batteries to establish electrical connections therebetween when the battery chamber lid 12 is closed.
In the above-described battery case that the assignee of the present invention has proposed, any member such as the aforementioned withdrawal battery-chamber forming member does not have to be drawn to the outside of the camera body, unlike the battery case shown in the aforementioned Japanese unexamined patent publication, which does not deteriorate not only the outward appearance of the camera but also the holding ease and the usability of the camera. However, since the difference in length (height) between the AA-sized cell and the CR-V3 battery is great, a problem arises in metal-to-metal contact between the aforementioned metal contacts on the battery chamber lid 12 and the associated electrodes of the battery when the battery chamber lid 12 is closed. FIGS. 16A and 16B show a cross sectional view of a part of the battery case 10 in which four AA-sized cells D1 are accommodated (only one of them appears in FIG. 16A) and a cross sectional view of a part of the battery case 10 in which two CR-V3 batteries are accommodated (only one of them appears in FIG. 16B), respectively, showing a comparison in a battery accommodated state therebetween. In the case where a resilient contact 112 is designed to have a spring force bringing the resilient contact 112 into proper contact with the positive electrode (+) of the associated relatively-short AA-sized cell D1 as shown in FIG. 16A, the degree of deformation of the resilient contact 112 becomes great when the relatively-long two CR-V3 batteries are used instead as shown in FIG. 16B to thereby cause the spring force exerted by the resilient contact 112 to become large. This large spring force (resiliency) of the resilient contact 112 acts on the battery chamber lid 12 at the bottom (upper end as viewed in FIG. 16B) of the associated CR-V3 battery, and accordingly, the battery chamber lid 12 needs to be closed by a relatively 1arge force when closed, which makes it difficult to close the battery chamber lid 12. In addition, since the spring force of the resilient contact 112 remains exerted on the battery chamber lid 12 when it is held closed, it is also difficult to release the engagement of the battery chamber lid 12 with the bottom wall 1a of the camera body 1 to open the battery chamber lid 12 by sliding the battery chamber lid 12 relative to the bottom wall 1a of the camera body 1.
Conversely, if the resilient contact 112 is designed to be capable of producing only a small spring force, the negative electrode (bottom electrode as viewed in FIG. 16A) of the AA-sized cell D1 shown in FIG. 16A and the positive electrode (bottom electrode as viewed in FIG. 16A) of another AA-sized cell D1 (not shown in FIG. 16A) adjacent to the AA-sized cell D1 shown in FIG. 16A are not properly in contact with an associated contact (not shown) which is fixed to an inner surface of the battery chamber lid 12 to make these two AA-sized cells connected serially when the relatively-short AA-sized cells are loaded into the battery case.